I want to install bathroom vents in my parents' upstairs bathrooms, since they don't have any and have mold issues.

The preferred area to have the vent exit the house is on the side, but the bathroom is dead center. It would be about a 30-foot run of duct. Is this ok? It's a small bathroom, about 6x12. I was thinking of using a 100CFM fan.

Also, since this attic is not finished, I take it I should be using special ductwork to keep it from freezing? Or do I just wrap metal 4" duct with fiberglass?

Thanks.

houseinthewoods

01-19-2010 08:48 PM

You would want to insulate the duct to prevent condensation inside the duct running back into the house. I've used the flexible insulated duct in my attic, but it was a short run (10').

30' seems like a long run. Can you not go straight up through the roof? I've never done it, but a recent episode of 'This Old House' demonstrated installing a fan vent in a shingle roof. He made it look easy. You might check their web site and see if the info is on line.

My other advise is the get the quietest fan possible. It will last a lot longer than the cheap builder-grade fans, and the family will use it. It will be significantly more expensive, but worth it.

Rick

jlhaslip

01-19-2010 08:54 PM

Albany New York gets a fair bunch of snow, so I would go out the gable end and not bother the roof.

secutanudu

01-19-2010 10:01 PM

I may be able to put a 4" hole in the soffit. It's not a very deep eave, so if it is not big enough, the only option is the gable, which is the 30' distance (i agree, do not want to put a hole in the roof). I want to get a quiet fan, but if the run is, in fact, 30 feet....how can I ensure the air will move all the way to the vent? Would I need another fan in the attic to help pull the air?

meboatermike

01-19-2010 10:23 PM

I personally would install a fan that is a higher cfm than you have figured. It will exhaust a greater volume quicker.

secutanudu

01-23-2010 09:14 AM

I will get the most CFM that I can stand, noise-wise. Is venting a bath fan through a soffit OK? Will moisture make its way back into the rest of the soffit vent into the attic?

Would it help or hurt things, if I go with a soffit vent, to tape over the soffit vent for a foot or two on either side of the new vent to prevent moisture from finding its way back in?

Never ever vent through a soffit. The moisture will enter back into the attic causing mold and mildew. The shorter the duct the better and use insulated ducting. The noise rates are in sones. Look for a fan with the lowest sones if you want a quiet fan. Panasonic are THE best all around fan, no ifs, ands, or buts about it. Roof would be a better option than running 30'. If you have snow issues, run the ducting up toward the top of the roof. If you do decide to vent through a gable, make sure you don't have sags and allow slope in case of moisture buildup.

Any thoughts on a 290CFM fan's ability to ven a 6x10 bathroom about 20 feet?

The run isn't quite as long as I thought it would be. This fan is a bit big, but only operates at 2 sones, seems like a good choice due to the long run.

Earnie

02-09-2010 12:17 PM

Never vent through a soffit?

If you must always vent through the roof, how do you keep snow from blocking the exhaust vent?

My bath exhaust fan is venting into the attic close to the soffit. I know it needs correcting. Was planning on soffit venting and as the OP mentioned and blocking the soffit air holes either side of exhaust grill.

secutanudu

02-09-2010 01:16 PM

Well since the bathroom is so small, I think the 290 CFM fan should be fine with the longer exhaust run (20 feet).

I'll probably go that route.

drtbk4ever

02-09-2010 02:28 PM

Quote:

Originally Posted by Earnie
(Post 397070)

Never vent through a soffit?

If you must always vent through the roof, how do you keep snow from blocking the exhaust vent?

My bath exhaust fan is venting into the attic close to the soffit. I know it needs correcting. Was planning on soffit venting and as the OP mentioned and blocking the soffit air holes either side of exhaust grill.

Correct, never vent through a soffit. That is almost as bad as having it directly vent into your attic. Either way, moist air will be circulating within your attic which will lead to all kinds of moisture problems, the least of which is mold.

Venting through the roof is the ideal solution. There are vent caps that are taller and reduce the likelihood of blockage from snow. Even then, the air coming out of the vent will be warm and moist. This will lead to the snow in the immediate vicinty to melt/sublimate.

Look where I live. We have roof vents for bathroom and kitchen exhaust and I have never known anyone to have an issue with snow.

But the final say should be what code requires for your area.

Earnie

02-09-2010 03:37 PM

Not questioning the wisdom or hands on experience here, just trying to understand the science behind it.

What's the difference between 95 degree, 100 percent humidity natural environmental air being drawn into the attic from the soffit and hot humid air from the bath fan vent?